An important concept in aging research concerns whether or not euploid cells have a finite or infinite proliferative capacity. The concept has been developed primarily in cell culture systems. The amphibian nuclear transplantation procedure (also known as cloning) provides the possibility of maintaining a euploid genome at a high proliferative rate for prolonged periods. The procedure also permits the replicating genome to reside in cells that retain their normal architecture; i.e., a nuclear transplant embryo consists of cells with normal 3 dimensional anatomy and the constituent cells are in appropriate contact one with another. The test protocol consists of inserting nuclei obtained from an appropriate genetically marked (triploid) blastula into activated and enucleated host ova. Normal cleavage ensues. The nuclear transplant blastula serves as a nuclear donor on day 2 and the procedure is repeated. The genome cloned on day 2 is identical to that of the original blastula donor. The process is repeated again on day 3 and serially thereafter until the experiment is terminated. At regular intervals, cloned embryos will be monitored for their ontogenetic capacity and abnormalities will be characterized if they occur. Karyoypes will be produced to provide evidence that the serially cloned embryos are in fact descended from the initial nuclear donor (as revealed by the cytogenetic marker) and to provide evidence that euploidy is maintained. Rana pipiens will be the species first studied and results with this species will be compared to results utilizing Bombina orientalis and Xenopus laevis.